Doctor in habit of fighting (6)

I believe the answer is:

combat

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'fighting' is the definition.
(I know that combat is a type of fighting)

'doctor in habit' is the wordplay.
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'in' is an insertion indicator.
'habit' becomes 'coat' (I can't explain this - if you can you should give a lot more credence to this answer).
'mb' inserted into 'coat' is 'COMBAT'.

'of' is the link.

Can you help me to learn more?

(Other definitions for combat that I've seen before include "A fight or contest, sometimes mortal" , "Fight against; fighting" , "Armed fighting" , "Conflict" , "Battle or fight" .)

I've seen this clue in The Guardian and The Globe and Mail.

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